The present invention relates to a cooling system for water-cooled engines installed in vehicles.
It is well known that water-cooled engines are universally used for vehicles, such as passenger cars and trucks. Such water-cooled engines are usually provided in front thereof with a cooling unit of the radiator type.
The cooling unit contains cooling water which is forcedly circulated through a channel interconnecting the cooling unit and the engine. The amount of the cooling water is conventionally as small as about 15 to about 16 liters (for 1200-2000 c.c. class in displacement). With use of such an amount of cooling water, the engine deteriorates abnormally rapidly especially during the hot season although operable free of noticeable troubles in the other seasons.
Stated more specifically, if a fully laden vehicle with the above-mentioned cooling water is driven on an upward slope during the hot season, the engine will develop the most serious trouble. Owing to the absolutely insufficient cooling capacity, heat builds up to an abnormal level in the piston-cylinder assembly, markedly impairing the characteristics of the lubricant to promote wear of the piston and cylinder. The enlarged clearance produced results in a lower compression ratio to reduce the power of the engine. The reduced compression ratio leads to impaired ignitability, deteriorates the plug and entails increased fuel consumption. Such problems are detrimental to savings in energy, pollution control and economical maintenance of the vehicle.
These problems are experienced especially with new vehicles and after cylinder boring. To effectively preclude the trouble resulting from the insufficient cooling water, the driver must avoid overloading during driving and break in the vehicle at a reduced speed, but such requirements are liable to be neglected and are fulfilled seldom in practice, so that the engine inevitably deteriorates rapidly.
Further with use of such an amount of cooling water as mentioned above, degradation of the lubricant permits rapid wear on the cylinder, piston, crankshaft and other sliding members of the engine, consequently reducing the endurance and performance of the engine assembly rapidly.
Additionally rust and other foreign matter are produced within the cooling unit in large quantities relative to the amount of the cooling water, with the resulting likelihood of clogging the water channel of the cooling unit to reduced the cooling effect and aggravate the foregoing problems.
Still further, the installation of two cooling units requires an increased space. Since the cooling unit comprises a radiator and a fan which must be driven by drive means, the additional cooling unit must be disposed in the vicinity of the existing cooling unit. Nevertheless, it is difficult to obtain such a large space within the bonnet (hood) of the vehicle. If it is attempted to provide the additional cooling unit outside the hood, an additional drive means needed results in a cost increase.
Thus, it is difficult in respect of space to install two cooling units in usual passenger vehicles. Also the arrangement is costly and, therefore, impractical because the cooling unit itself is so expensive and necessitates the drive means for the fan.
Furthermore, when the temperature of the engine is conventional, there is the need to maintain the piston-to-cylinder clearance at 5/100 mm, but the clearance of 5/100 mm entails a reduced engine output and an increased amount of fuel consumption. If the clearance is 3/100 mm, the engine gives a maximum output and achieves a reduction in the amount of fuel consumption. To enable the engine to rotate properly without seizure at the clearance of 3/100 mm, the engine must be maintained at a temperature of 30.degree. to 50.degree. C., so that it is very critical to maintain the engine temperature at 30.degree. to 50.degree. C.